FIG. 1 describes an example of a logging installation in a horizontal well 1. A probe supporting device 3 comprises a male electrical connector 4 connected by conductors to logging probes 2. A load bar 5 comprising at its lower end a female electrical connector is lowered in drill string 7 by means of an electrical cable 6 referred to as logging cable. The load bar and the cable are displaced through pumping in the highly deflected part of the well until they reach the male connector of the probe supporting device. Connection between the two elements of the electrical connector provides electrical continuity between the logging probes and surface recording equipment 10. Once the female connector in place on the male connector, the operators screw on a side-entry sub 8 allowing to pass the logging cable into the annular space between the well and the string. Thus, descent and/or displacement of the probes is achieved by assembling or by removing drill string pipes 11. Reference number 9 relates to the conventional well shutoff means the wellhead is equipped with.
During the logging operation using a drill string, the pressure of the fluid in the geologic formation is balanced by the hydrostatic pressure of the fluid, notably the drilling fluid, contained in the rods and outside the rods.
In case of unbalance, sudden fluid inflows from the formation can be difficult to control. Fluid upwelling through the annulus can be controlled by seal assembly 9.
Fluid upwelling can however occur through the inside of the drill rods. In fact, the logging systems currently used allow circulation of the drilling fluid, notably to cool the well, to renew the drilling fluid, maintain the pressure balance with the geologic formation crossed, and also to pump and displace the load bar in the inner space of the drill rods. The equipment currently used allows free circulation in both directions within the drill string.
The object of the present invention is to overcome risks of sudden circulation, in the opposite direction from the bottom upwards, within the rods during horizontal logging operations, because such circulation may notably cause a blowout at the surface or disconnection of the male and female connectors.